Field of the Invention
The present invention is generally directed toward pyrotechnic devices in which the primary pyrotechnic charge is hermetically sealed within the device for storage under ambient temperature conditions, but is configured to be vented when exposed to elevated-temperature conditions, such as might be encountered in extreme downhole environments. The devices comprise a passage between an internal chamber containing the pyrotechnic charge and the exterior of the device that is normally sealed with a temperature-sensitive material. Upon exposure to elevated-temperature conditions, the temperature-sensitive material releases thereby opening the passage so that off gases generated by the pyrotechnic material upon exposure to high temperatures may be vented away, thereby slowing the thermal deactivation of the pyrotechnic material.
Description of the Prior Art
Explosive materials are often utilized in oil well completion operations, such as in perforating the well casing to permit communication of the underground formation with the well bore. Often, pyrotechnic devices are used to initiate detonation of these explosive materials. These pyrotechnic devices can include fuses comprising time delays that are ignited with an igniter device. Actuation of the igniter device results in ignition of an output charge that in turn ignites a further pyrotechnic device, such as the aforementioned fuse. The output charge comprises a pyrotechnic material, such as lead azide, lead styphnate, and 2,2′,4,4′,6,6′-hexanitrostilbene (HNS-II).
Downhole environments can be quite extreme as compared to conditions at the surface. It is not uncommon for temperatures downhole to exceed 200° F., particularly at extreme depths of 5000 ft. or more. Prolonged exposure to prolonged elevated temperatures can result in the thermal decomposition of the pyrotechnic material used in the initiator. This thermal decomposition generally results in the generation of gaseous products, such as nitrogen, oxygen, and ammonia, depending upon the composition of the pyrotechnic material present in the initiator. Typically, the thermal decomposition of the pyrotechnic material at elevated temperatures as might be encountered downhole progresses slowly. However, the presence of these off gases further accelerates deactivation of the pyrotechnic material at the elevated temperature conditions. If a significant period of time passes between downhole insertion and use of the igniter device, the pyrotechnic material may have degraded to the extent that it no longer is capable of ignition or providing a sufficient explosive output leading to operational downtime.
Thus, there exists a need in the art for an igniter device capable of prolonged exposure to downhole elevated-temperature conditions without the pyrotechnic material contained therein becoming deactivated.